Autoreactive CD4+ T cells are present at low frequency in peripheral blood, often with low antigen avidity,[unreadable] and show reactivity to multiple autoantigens. Nevertheless, they are central determinants of autoimmunity,[unreadable] guiding not only specificity and magnitude of immune responses, but also critically involved in the balance[unreadable] between disease progression and regulation. We propose to exploit recent advances in several areas?[unreadable] multimer technology, T1D prediction, cellular microarrays, and humanized mouse models?in order to[unreadable] develop profiles for islet antigen-reactive T cells associated with T1D susceptibility, disease, and protection.[unreadable] In Aim 1, HLA class II tetramers (for six islet antigens) and class I tetramers (for two islet antigens) will be[unreadable] used together with flow cytometry techniques to compare T cell characteristics among well-characterized[unreadable] human subjects at risk for T1D or with progressive disease; In Aim 2, we will analyze the functional[unreadable] properties of one of the important phenotypes associated with T1D?namely, the low avidity autoreactive[unreadable] CD4+ T cells. A partially humanized mouse model created for this purpose will enable a detailed evaluation[unreadable] of the activation and homing properties. In Aim 3, new technologies designed to translate research[unreadable] techniques into more sensitive and rapid clinical tests will be developed, in order to advance T cell profiling[unreadable] into a more useful clinical research tool. These studies will be closely integrated with other elements of the[unreadable] Autoimmunity Cooperative Group, both at UCHSC and at other sites, and the resources derived in this[unreadable] project will be disseminated to the other sites, as well.